The present invention broadly relates to manually operated control elements, such as levers and pedals, and deals more particularly with an arrangement for eccentric mounting of a lever return spring.
Hand and foot operated control levers used in a variety of applications often employ spring loading to cause the lever to return to a starting or home position. In one typical configuration, the lever is pivotally mounted by a shaft carried on a stationary base or bracket, and the return spring is in the firm of a helical coil wrapped around and concentric with the shaft. The outer end of the coil spring is connected with the lever, while the opposite end of the spring is secured to the bracket, thus biasing the lever to move to its home position, but yieldable to the force applied by an operator to move to an intermediate or fully actuated position.
Concentric mounting of a coil spring in a control lever assembly of the type mentioned above results in several problems. First, because of the locations at which the opposite ends of the spring are loaded, the resultant forces applied to this spring tend to cause the spring to shift laterally in one direction away from the shaft. This lateral shifting of the spring when the lever is displaced causes uneven loading of the spring and related mounting components because the forces and resulting stresses are not evenly distributed. Consequently, components of the lever assembly are subject to premature failure.
Another adverse consequence of lateral shifting of the spring during lever operation is that adjacent coils of the spring often come in contact with each other, and as the lever continues to move during a stroke, the contacting coil segments rub against each other, causing spring wear. In applications where the control lever is subjected to heavy cycling, wearing of the spring in this manner can result in spring failure, in which case the control lever remains in its partially actuated state, rather than returning to its home position under the influence of the spring force.
One common application of a control lever of the type described above involves throttle controls, such as throttle control pedals used on vehicles where the pedal may be operated millions of cycles under heavy duty use typical of commercial vehicle applications. Certain of these throttle pedals, rather than being mechanically linked to vehicle""s engine, rely on an electronic sensor mounted on the pedal to sense pedal position and deliver an electrical signal to the engine representative of such position. Return spring failure can be particularly serious in so called xe2x80x9celectronicxe2x80x9d throttle pedal applications since failure of the pedal to return to its home or idle position means that the vehicle engine continues to receive a throttle command signal somewhere between idle and wide open throttle. In the past, the only solution to reducing spring failure occasioned by rubbing of adjacent spring coils has been to lubricate the coils to reduce friction therebetween. Lubrication can be achieved by applying a Teflon coating to the spring. This Teflon coating, however, increases the cost of the pedal assembly, and even where effective, does not eliminate the problem of failure of the spring in other components due to the uneven loading of these components when the spring moves laterally during a pedal stroke.
Accordingly, there is a clear need in the art for an improved arrangement for mounting the coil spring in a manner which eliminates uneven distribution of spring loads and stresses, and avoids face-to-face contact of adjacent coils of the return spring. The present invention is directed toward satisfying this need.
According to one aspect of the invention, an improved arrangement for mounting a helically coiled return spring on the end of a control lever includes a spring mounting perch eccentrically mounted relative to a shaft that pivotally supports one end of the lever. The spring surrounds the shaft and has its inner and outer ends respectively secured to the perch and one end of the lever, thereby biasing the lever to a home or idle position. Eccentric positioning of the perch, and thus of the inner end of the spring, assures even spring load distribution and prevents coil-to-coil spring contact.
According to another aspect of the invention, a foot pedal control is provided, comprising: a pedal; a housing carried on one end of the pedal; a base; a helical return spring for returning the pedal to a home or idle position; a shaft mounting the pedal for rotation; means for connecting the spring between the base and the housing; and means for restraining the spring against lateral movement.
The restraining means preferably comprises a rib-like projection extending inwardly from an inside wall of the lever housing, and engagable with the outside coil of the spring to restrain the coil against lateral shifting during actuation of the pedal.
Accordingly, it is a primary object of the present invention to provide an improved arrangement for mounting a helical return spring on a control lever which assures even loading of the spring and related mounting components, while at the same time avoids coil-to-coil contact and resultant wear of the spring.
A further object of the invention is to provide an improved spring mounting arrangement as described above which eliminates the need for lubrication of the spring coils necessary to reduce frictional engagement therebetween.
A still further object of the present invention is to provide a return spring mounting arrangement of the type mentioned above which requires minimal modification of existing lever designs.
A still further object of the invention is to provide a foot pedal assembly having a return spring that exhibits increased service life and reduced component cost.
These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.